Coffee Pest May Harbor Its Weakest Link

Bacteria named Wolbachia may be the key to discovering why the coffee berry borer (CBB) is such a destructive insect pest of the coffee bean, causing an estimated $500 million in annual losses worldwide. Agricultural Research Service scientist Fernando Vega in the Insect Biocontrol Laboratory in Beltsville, Md., is studying the relationship between the bacteria and CBB.

Adult females enter the coffee berry and deposit their eggs; larvae feed on the coffee bean, lowering its quality or causing the entire berry to fall off. A skewed, 10-to-1 sex ratio favoring females ensures high reproduction and greater berry damage. Adult females emerge from the berry already inseminated, taking less than one day to enter another berry and start depositing eggs. This life cycle makes the insect an extremely difficult candidate for integrated pest management programs.

But why are there so many females? Research suggests that Wolbachia might play a role in sex determination. This bacterium has been widely reported to affect insect sex ratios; skewed sex ratio is observed in CBBs throughout the world. No other bacterium is known to have such an effect on sex ratio.

Researchers collected CBBs from 16 countries: Benin, Brazil, Cameroon, Colombia, the Dominican Republic, Ecuador, El Salvador, Honduras, India, Indonesia, Jamaica, Kenya, Mexico, Nicaragua, Uganda and Peru. Genetic analysis done in collaboration with Pablo Benavides and Jeff Stuart of Purdue University and Scott O’Neill of the University of Queensland, Australia, indicates Wolbachia is present in CBBs originating from 11 of the countries. Wolbachia was not detected in CBBs from five of these countries, but a genetic variation may make it undetectable using current tests.

Additional studies confirming the elimination of the female-biased sex ratio in the offspring of CBB females treated with antibiotics would support the hypothesis that Wolbachia is indeed involved in sex determination. Understanding the relationship between the CBB and Wolbachia may provide insight into the basic biology of the insect, perhaps leading to possible microbial controls.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.